a) Field of the Invention
The present invention relates to dry etching of Si (silicon)-containing material suitable for manufacture of LSIs or other semiconductor devices, and more particularly to a dry etching method and system capable of reducing particles.
b) Description of the Related Art
An ECR (electron cyclotron resonance) plasma etching system such as shown in FIG. 3, a microwave plasma etching system such as shown in FIG. 4, and other systems are known as conventional means for dry etching Si-containing material.
In the etching system shown in FIG. 3, a process chamber 10 defines a reaction chamber 10b and a plasma chamber 10a. An anti-deposition plate 12 usually made of quartz is mounted on the inner wall of the process chamber 10.
A susceptor (electrode) 14 is disposed at the bottom of the reaction chamber 10b, for placing thereon a wafer 16. A high frequency power source 18 is connected to the susceptor 14 to supply a high frequency power of, for example, 13.56 MHz. The reaction chamber 10b is coupled via a pipe 26 to an unrepresented gas supply source, and connected at its bottom side to an unrepresented vacuum pump VAC.
To the upper space of the reaction chamber 10a, a microwave .mu.W of, for example, 2.45 GHz, is supplied from a microwave source not show in the drawing via a microwave guide window 20 usually made of quartz. A solenoid coil 22 is disposed surrounding the upper portion of the process chamber 10 for applying a magnetic field in the process chamber 10.
In the etching system shown in FIG. 4, etching gas EG is supplied to a process chamber 30 confined in a vessel 32 made of quartz or a different kind of material, the bottom of the chamber 30 being connected to an unrepresented vacuum pump VAC.
A susceptor (electrode) 34 is disposed in the process chamber 30, for placing thereon a wafer 36. A high frequency power of, for example, 2 MHz, is supplied from a high frequency power source 38 to the susceptor 34 to generate a bias electric field.
A microwave of, for example, 2.45 GHz, is supplied from a magnetron 40 via a waveguide 42 to the upper space of the process chamber 30. A solenoid coil 44 is disposed surrounding the upper portion of the process chamber 30 for establishing a magnetic field in the process chamber 30.
Silicon oxyhalide (SiO.sub.x X.sub.y, where X is Cl, or Br) by-products are generated while Si-containing material is etched by plasma of mixed gas in the dry etching systems shown in FIGS. 3 and 4. The Si-containing material may be monocrystalline Si, polycrystalline Si, amorphous Si, refractory metal silicide (WSi.sub.2, MoSi.sub.2, TiSi.sub.2, TaSi.sub.2), or other materials, and the mixed gas is a mixture of oxygen gas and halogen (Cl, Br) containing gas, such as Cl.sub.2 /O.sub.2, HBr/O.sub.2, HCl/O.sub.2). O.sub.2 gas is mixed in order to form an anisotropic pattern shape and improve an etching selection ratio of SiO.sub.2. Si oxyhalide serves to protect a pattern side wall and form an anisotropic pattern shape.
Si oxyhalide is also attached to the inner wall of the process chamber and generates particles in the following mechanism. Although the inner wall of the process chamber is heated by microwave during etching, it is not heated while microwave is not supplied (such as when a wafer is placed in or taken out of the process chamber). Therefore, it undergoes a temperature cycle during the supply and stop of microwave. Si oxyhalide attached to the inner wall of the process chamber during etching is peeled off from the inner wall of the process chamber when the temperature of the process chamber lowers, because of a thermal expansion coefficient difference between the inner wall and Si oxyhalide, and generates particles which drop onto the wafer and contaminate it.
Wafer contamination by particles results in a low product yield. In view of this, etching Si-containing material starts generally after the process chamber is subjected to a cleaning process. The cleaning process includes wet cleaning and dry (or plasma) cleaning. Normally, after wet cleaning is performed, dry (or plasma) cleaning is performed. This dry (or plasma) cleaning is also called aging. With this aging, a wafer (e.g., a bare wafer without pattern) prepared for aging only is plasma-etched under the same conditions as etching a product wafer in order to obtain the same atmosphere as etching the product wafer and stabilize the following actual process of etching the product wafer.
The following three methods (a) to (c) have been proposed for such aging:
(a) an Si bare wafer is used as an aging wafer, and etched by plasma of mixed gas of O.sub.2 gas and Cl- or Br-containing gas;
(b) an Si wafer with a photoresist layer is used as an aging wafer, and etched by plasma of mixed gas of O.sub.2 gas and Cl- or Br-containing gas; and
(c) an Si wafer with a refractory metal silicide layer such as WSi.sub.2 and a photoresist layer formed in this order is used as an aging wafer, and etched by plasma of mixed gas of O.sub.2 gas and Cl- or Br-containing gas.
With the above methods (a) and (b), Si oxyhalide by-products are attached to the inner wall of a process chamber and generate particles in the way of the above-described mechanism.
With the above method (c), not only Si oxyhalide by-products are generated, but refractory metal halide or oxyhalide by-products are also generated when refractory metal silicide is etched. This method also poses the problem of particles as in the methods (a) and (b).
These conventional aging methods all have the possibility of generating particles.
As a conventional method of preventing particles from being scaled off an anti-deposition plate in a process chamber of a dry etching system or film forming system, it is known to cover a film attached to the anti-deposition plate with a protect layer which is good in adhesion with the attached film (e.g., Japanese Patent Laid-open Publication No. 3-29324).
Even with this particle preventing method, it is difficult to refrain from the generation of particles of Si oxyhalide by-products dropped from the inner wall of the process chamber, when Si-containing material is etched by plasma of mixed gas of O.sub.2 gas and halogen (Cl, Br)-containing gas. Namely, even if a protect film good in adhesion with the Si oxyhalide film is formed, it is difficult to prevent the Si oxyhalide film from being flaked during the Si-containing material etching process.